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Math Help - real solutions and mathematical model

  1. #1
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    Unhappy real solutions and mathematical model

    I'm having trouble with a few of my homework problems this evening. *sigh*

    1. Find all real solutions of x4 - 7x3 + 7x + 21x - 30 = 0

    and

    2. Find a mathematical model representing the statement. (In each case determine the constant of proportionality.)
    F varies directly as x and inversely as y, and F = 500 when x = 15 and y = 2


    I thought number one would be easy. I guess I was wrong.
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  2. #2
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    Quote Originally Posted by uglygreencouch View Post
    I'm having trouble with a few of my homework problems this evening. *sigh*

    1. Find all real solutions of x4 - 7x3 + 7x + 21x - 30 = 0

    .
    Do rational roots theorem and see what you get.
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  3. #3
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by uglygreencouch View Post
    I'm having trouble with a few of my homework problems this evening. *sigh*

    1. Find all real solutions of x4 - 7x3 + 7x + 21x - 30 = 0
    as TPH says, use the rational roots theorem. the factor theorem will also come in handy, you can look these up on wikipedia. if you still have problems, just say so

    2. Find a mathematical model representing the statement. (In each case determine the constant of proportionality.)
    F varies directly as x and inversely as y, and F = 500 when x = 15 and y = 2
    F varies directly as x means F = k_1x for some constant k_1.

    when F = 500, x = 15, use this to find k_1 and then plug it into the original equation to find the model.

    do a similar thing with the second case, just note that F varies inversely as y means F = \frac {k_2}y for some constant k_2
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  4. #4
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    thanks guys
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